Adds more details, background throughout

By David Shepardson

WASHINGTON, Feb 11 (Reuters) - The U.S. Federal Aviation Administration took the extraordinary step of barring all flights to and from Texas' El Paso International Airport, which borders Mexico, for 10 days, citing "special security reasons," stranding numerous planes and thousands of travelers.

The action barring flights at a single U.S. airport appear unprecedented, government officials said. After the Sept. 11, 2001 attacks, the FAA barred all civilian flights across the United States for several days.

Airline sources told Reuters the grounding of flights was believed to be tied to the Pentagon's use of counterdrone technology to address Mexican drug cartels' use of drones of the U.S.-Mexico border. The flight prohibition also covers some rural air space in neighboring New Mexico.

The move has stranded numerous aircraft from Southwest Airlines and American Airlines at the airport among other airlines.

El Paso airport handles about 4 million passengers yearly.

The El Paso airport confirmed the development in an Instagram post.

NATURE OF SECURITY REASONS NOT SPECIFIED

The FAA did not specify the nature of the "security reasons" and declined to comment beyond the notice. It said the temporary restrictions would be in place until February 21. It does not apply below 18,000 feet (5,486 meters), which allows airplanes to transit over the airspace.

The FAA could opt to extend the alert. Airlines were caught off-guard by the announcement, which occurred early Wednesday.

In mid-January, the FAA warned airlines to exercise caution when flying over Mexico, Central America and parts of South America, citing the risks of potential military activities. That caution was lifted last week after Trump said the United States wanted flights to resume to Venezuela.

Tensions between the U.S. and regional leaders have ramped up since the Trump administration mounted a large-scale military buildup in the southern Caribbean, attacked Venezuela and seized its president, Nicolas Maduro, in a military operation.

Trump said in January that drug cartels were running Mexico and suggested that the U.S. could strike land targets to combat them, in one of a series of threats to deploy U.S. military force against cartels.

After the attack on Venezuela, the FAA curbed flights throughout the Caribbean, forcing the cancellation of hundreds of flights by major airlines.

In December, a JetBlue passenger jet bound for New York took evasive action to avoid a mid-air collision with a U.S. Air Force tanker plane near Venezuela, which did not have its transponder activated.